CODEWITHSUNDEEP
mongodb
daydreamer
daydreamer

Reputation: 91959

MongoDB : getting list of values by using Group

I have a collection called contract and I would like to group using "a_id" 

{
 a_id: 1,
 "name": "n1"
}
{
 a_id: 2,
 "name": "n2"
}
{
 a_id: 1,
 "name": "n3"
}
{
 a_id: 1,
 "name": "n4"
}
{
 a_id: 2,
 "name": "n5"
}

I want to group by "a_id" to show me the list of names associated.

{
 a_id: 1,
 values: ["n1", "n3", "n4"]
}
{
 a_id: 2,
 values: ["n2", "n5"]
}

My code: 

db.contract.group({ 
      key:{a_id: 1}, 
      initial: {v: ''}, 
      reduce: function(doc, obj){ 
            v = v + " " + obj.name
      } 
});

My Output:

{
        "a_id" : 1,
        "v" : ""
    },
    {
        "asset_id" : 2,
        "v" : ""
    }

This doesn't return the list of values, but mongd logs shows me list of names, How can I correct this?

Fixed 

db.contract.group({
   key:{a_id: 1}, 
   initial: {v: []}, 
   reduce: function(obj, prev){ 
      prev.v.push(obj.name)
   }
});

Upvotes: 5

Views: 4177

Answers (2)

sektoid0
sektoid0

Reputation: 141

You could also use MongoDB's aggregation framework:

The following will work exactly the same:

db.contract.aggregate({$group: { '_id': '$a_id', 'name': { $push: '$name'}}})

The following will put every unique value only once in the result set (in case there are duplicated names per 'a_id'):

db.contract.aggregate({$group: { '_id': '$a_id', 'name': { $addToSet: '$name'}}})

Upvotes: 14

daydreamer
daydreamer

Reputation: 91959

Fixed 

db.contract.group({
   key:{a_id: 1}, 
   initial: {v: []}, 
   reduce: function(obj, prev){ 
      prev.v.push(obj.name)
   }
});

Upvotes: 1

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